Question

A motorboat travels 10 km downstream in 50 minutes and returns in 1 hour. What is the speed of the motorboat in still water? ​

Answer 1

Answer:

speed = distance/time

speed in upstream = 10/1 = 10km/hr

speed in downstream = 10/50/60 = 10×60/50

= 60/5 = 12km/hr

speed in still water = 1/2( speed in downstream + speed in upstream )

= 1/2(12+10)

1/2 × 22

= 11

speed in still water is 11km/hr

Answer 2

The speed of the motorboat in still water is 11 km/h.

A motorboat travels 10 km downstream in 50 minutes and returns in 1 hour.

We have to find the speed of the motorboat in still water.

• Let, speed of motorboat in still water = x km/h and speed of current = y km/h.

• for downstream, speed of motorboat = (x + y) km/h
• for upstream, speed of motorboat = (x - y) km/h

∵ The motorboat travels 10 km downstream in 50 min.

⇒distance/speed = time [we know ]

⇒10km/(x + y) km/h = = 50 min = (50/60) hr

⇒10/(x + y) = 5/6

⇒x + y = 12 ....(1)

Again, The motorboat returns (means, upstream) in 1 hr.

⇒10/(x - y) = 1

⇒x - y = 10 ....(2)

From equations (1) and (2) we get,

⇒x = 11 and b = 1

Therefore the speed of the motorboat in still water is 11 km/h.

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